Vehicle power transmission device and control system for power transmission

ABSTRACT

A power transmission apparatus for a vehicle which includes a first, a second, and a third rotor which split power among a motor-generator, an internal combustion engine, and a driven wheel of the vehicle. The apparatus also includes a torque transmission control mechanism which selectively transmits torque between the first rotor and the engine. When the torque transmission control mechanism establishes the transmission of torque between the first rotor and the engine, powers, as produced by the second and third rotors, are opposite in sign to each other. This enables the speed of the first rotor to be set to zero (0) or a very low speed. Therefore, when an initial torque is applied to the engine through the first rotor to start the engine, the mechanical vibration which usually arises from the application of initial torque and is to be exerted on the power transmission apparatus is minimized.

CROSS REFERENCE TO RELATED DOCUMENT

The present application is divisional of U.S. application Ser. No.12/947,138, filed Nov. 16, 2010, now allowed, which claims the benefitsof Japanese Patent Application No. 2009-261385 filed on Nov. 16, 2009,the disclosures of each of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Technical Field of the Invention

The present invention relates generally to a vehicle power transmissiondevice equipped with a plurality of power split rotors which work tosplit output power or torque among an electric rotating machine (e.g., adynamo-electric machine), an internal combustion engine, and drivenwheels of a vehicle and are designed to rotate in conjunction with eachother and a power transmission control system for such a powertransmission device.

2. Background Art

In recent years, in terms of reducing the amount of energy consumed byautomotive vehicles, so-called hybrid vehicles have been put intopractical use which are equipped with an electric rotating machine suchas an in-vehicle power source functioning as both an electric motor anda generator in addition to an internal combustion engine. The hybridvehicles are typically controlled to stop the internal combustion enginein a low speed running range in view of the fact that the internalcombustion engine is usually inefficient in energy use at low speeds.However, the hybrid vehicles face difficulties in starting the internalcombustion engine during running of the vehicles. For example, it isdifficult to bring a rotor which is coupled with driven wheels of thevehicle and rotating at a relatively high speed into mechanicalconnection with the crankshaft of the internal combustion engine whichis stopped.

In order to avoid the above problem, there have been in practical usehybrid vehicles equipped with an electric motor whose output shaft isconnected directly to a crankshaft of the internal combustion engine totransmit the torque, as outputted from the electric motor, to thecrankshaft to start the engine. After start-up of the engine, thetorque, as produced by the engine, is transmitted to the driven wheelsof the vehicle.

Additionally, there have been in practical use hybrid vehicles equippedwith a typical planetary gear speed reducer (also called an epicyclereduction gear train) made up of three power split rotors: a sun gear, acarrier (also called a planetary carrier), and a ring gear which work tosplit power or torque among the electric rotating machine, the internalcombustion engine, and the driven wheels of the vehicle. The drivenwheels and the electric rotating machine are coupled mechanically to thering gear. The generator is coupled mechanically to the sun gear. Theinternal combustion engine is coupled mechanically to the carrier. Inoperation, when torque is applied to the sun gear or the ring gear, thecarrier is rotated, thereby rotating the rotating shaft (i.e., thecrankshaft) of the internal combustion engine. The internal combustionengine is started by the output torque of the carrier. After thestart-up of the internal combustion engine, the engine torque istransmitted to the driven wheels of the vehicle through the carrier.

For example, Published Japanese translation of International PatentApplication No. 2004-514103 teaches the above type of power split rotorswhich split power between a main engine installed in the vehicle anddriven wheels of the vehicle.

The direct coupling of the rotating shaft of the electric motor to thatof the internal combustion engine, as described above, will cause thetorque load to be exerted by the internal combustion engine on theelectric motor when the internal combustion engine is not fired, butbeing free-wheeling or when the engine is being cranked by the electricmotor, thus resulting in an increase in energy consumption in thevehicle. A problem is also encountered in that the pulsation of torqueoccurring at the rotating shaft of the internal combustion engine whenstarted may result in a decrease in driveability of the vehicle.

Further, the use of the planetary gear speed reducer leads to theproblem that starting of the internal combustion engine when therotational speed of the carrier is low will cause the internalcombustion engine to be kept run at a low speed for a while. This isagainst the intended purpose of the hybrid vehicles which is to run theinternal combustion engine in a speed range in which the engineefficiency is high.

SUMMARY OF THE INVENTION

It is, therefore, a principal object of the invention to avoid thedisadvantages of the prior art.

It is another object of the invention to provide a power transmissionapparatus for a vehicle which is equipped with power split rotors tosplit power or torque among an electric rotating machine, an internalcombustion engine, and a driven wheel of the vehicle and designed toensure the startability of the internal combustion engine.

According to one aspect of the invention, there is provided a powertransmission apparatus for a vehicle equipped with an electric rotatingmachine, an internal combustion engine, and at least one driven wheel.The power transmission apparatus comprises: (a) a power split devicewhich includes a first, a second, and a third rotor which are rotate inconjunction with each other to split power among an electric rotatingmachine, an internal combustion engine, and a driven wheel of thevehicle, the first, the second, and the third rotor being so linked asto have rotational speeds thereof arrayed on a straight line in anomographic chart; (b) a torque transmission control mechanism whichselectively establishes and blocks transmission of torque between thefirst rotor and the internal combustion engine; (c) a connectingmechanism which establishes a mechanical connection between the secondrotor and the third rotor; and (d) a speed variator which has a variableinput-to-output speed ratio. When the torque transmission controlmechanism establishes the transmission of torque between the first rotorand the internal combustion engine, powers of the second and thirdrotors, are opposite in sign to each other.

In other words, the power split device is so designed that the powers ofthe second and third rotors are opposite in sign to each other when thetorque is transmitted from the first rotor to the internal combustionengine through the torque transmission control mechanism. The power is,therefore, circulated between the second and third rotors, thus enablingthe speed of the first rotor to be set to zero (0) or a very low speedor the power of the first rotor to be decreased to a very low leveleasily. Therefore, for example, when the engine is at rest, and it isrequired to apply initial torque to the internal combustion enginethrough the first rotor to start the internal combustion engine, a rateat which the torque to be applied to the engine is increased may bechanged slowly, thus minimizing mechanical vibrations which occur whenthe engine is being cranked and are to be transmitted to the powertransmission apparatus, the driven wheels, and the operator of thevehicle. After completion of the application of initial torque to theinternal combustion engine through the first rotor, the torque, asproduced by the internal combustion engine, may be outputted to thepower split device (i.e., the first rotor or other rotors).

The power will be circulated between the second and third rotors at atime when they are connected mechanically by the connecting mechanism.The above setting of the signs is, therefore, achieved easily withouthaving to two electric rotating machines: one having an input to whichpower is inputted from one of the second and third rotors, and thesecond outputting rotational energy to the other of the second and thirdrotors.

The inclination of the straight line in the nomographic chart may beregulated by changing the input-to-output speed ratio of the speedvariator. In other words, the speed of the first rotor may be controlledby changing the input-to-output speed ratio of the speed variatorregardless of the speed of the driven wheel. It is, therefore, possibleto control the speed of the first rotor when it is required to transmittorque from the first rotor to the internal combustion engine throughthe torque transmission control mechanism.

In the preferred mode of the invention, the electric rotating machineand the driven wheel are coupled mechanically to the second and thirdrotors which are to be connected together by the connecting mechanism.

Torques, as produced by the first rotor, the second rotor, and the thirdrotor, are proportional to each other. In other words, the power splitdevice is so designed as to exhibit such a torque relation.

The electric rotating machine is connected mechanically to the secondrotor without through the speed variator. The driven wheel is coupledmechanically to the third rotor without through the speed variator. Whenit is required to transmit an output of the electric rotating machine tothe driven wheel without the power split device, the speed of the outputof the electric rotating machine may changed by the speed variator.

The power transmission apparatus may further comprise a torque applyingmechanism which establishes a mechanical connection between the secondrotor and the internal combustion engine to apply torque, as produced bythe internal combustion engine, to the second rotor. Specifically, thefirst rotor serves as an engine starting rotor to be coupled to theinternal combustion engine when starting the engine. The second rotorserves as a power transmitted rotor which is to be coupled to theinternal combustion engine and to which torque is transmitted from theinternal combustion engine. The engine starting rotor is different fromthe power transmitted rotor, thus enabling the speed of the internalcombustion engine to be brought to an effective speed range quickly.

The torque applying mechanism is adapted to connect the internalcombustion engine to the second rotor without through the speedvariator. The torque applying mechanism serves as a one-way torquetransmission mechanism which has an input leading to the internalcombustion engine and an output leading to the second rotor and works totransmit the torque from the input to the output when speed of the inputis higher than that of the output.

A smooth mechanical connection of the internal combustion engine to thesecond rotor to transmit torque to the second rotor after the internalcombustion engine is started up may be achieved by bringing speeds ofthe internal combustion engine and the second rotor into agreement witheach other and then joining them together. This, however, requires finespeed control. In contrast, the one-way torque transmission mechanismstarts to transmit the torque from the internal combustion engine to thesecond rotor when the speed of the input of the one-way torquetransmission mechanism reaches that of the output. In other words, thepulsation of torque occurring when the engine is being started is nottransmitted to the power transmission apparatus until the speed of theengine reaches that of the second rotor, thus avoiding the transmissionof mechanical vibration from the engine to the power transmissionapparatus, the driven wheel, or the operator of the vehicle.

The power transmission apparatus may further comprise a secondconnecting mechanism which establishes a mechanical connection betweenthe first and second rotors through a second power transmission path,and a second varaitor with a variable input-to-output speed ratiodisposed in the second power transmission path. A first connectingmechanism that is the connecting mechanism to connect the second andthird rotors mechanically through a first power transmission path inwhich a first speed variator that is the speed variator is disposed andthe second connecting mechanism are controlled in operation to switchbetween a first operation mode and a second operation mode. The firstoperation mode is to establish the mechanical connection between thesecond and third rotors through the first connecting mechanism and blockthe mechanical connection between the first and second rotors throughthe second connecting mechanism. The second operation mode is to blockthe mechanical connection between the second and third rotors throughthe first connecting mechanism and establish the mechanical connectionbetween the first and second rotors through the second connectingmechanism.

When a sign of speed of the electric rotating machine is set to be oneof plus and minus, signs of powers, as produced by the first and secondrotors, are opposite to each other in the first operation mode, andsigns of powers, as produced by the second and third rotors, areidentical with each other in the second operation mode. In the firstoperation mode, the power is circulated between the first and secondrotors since the signs of the powers of the first and second rotors areopposite to each other. The circulation of power may establish thegeared neutral which places the speed of the third rotor at zero (0)even when absolute values of speeds of the first and second rotors aregreater than zero (0), but has the disadvantage that the efficiency inusing the energy. Therefore, it is not desirable to place the powertransmission apparatus in the first operation mode when the disadvantagebecomes great. In the second operation mode, the power is not circulatedbetween the second and third rotors. The power transmission apparatusswitches from the first operation mode in which the power is circulatedto the second operation mode in which the power is not circulated undercondition that the signs of the speeds of the first and second rotorsare fixed. In other words, the power transmission apparatus may switchthe operation thereof from the condition in which the power iscirculated to the condition in which the power is not circulated withoutreversing the speed of the electric rotating machine.

The sign of power, as referred to herein, indicates whether the power isinputted to or outputted from each of the first to third rotors.

The first and second speed variators maybe implemented by a single speedvariator such as a CVT.

A power transmission path is provided between one of the internalcombustion engine and the electric rotating machine and the drivenwheel. A first order derivative value of a function, in which theinput-to-output speed ratio of the speed varaitor is expressed by anindependent variable, and a total input-to-output speed ratio of thepower transmission path is expressed by a dependent variable, withrespect to the independent variable in the first operation mode isopposite in sign to that in the second operation mode. This enables thetotal input-to-output speed ratio to be changed to have values differentbetween the first and second operation modes by changing a direction inwhich the input-to-output speed ratio of the speed variator is changedin the second operation mode to be opposite a direction in which theinput-to-output speed ratio of the speed variator is changed in thefirst operation mode when the first operation mode is switched to thesecond operation mode. This results in an increased range in which thetotal input-to-output speed ratio is permitted to be changed, thusallowing the power transmission apparatus to be reduced in size.

The power transmission apparatus may also include a first-to-second modeswitching speed variator which works to change the speed of at least oneof the second and third rotors for compensating for a difference inspeed between the second and third rotors when the first operation modeis switched to the second operation mode to establish the mechanicalconnection between the second and third rotors. Specifically, an inputspeed of the second connecting mechanism may be identical with an outputspeed of the second connecting mechanism. This eliminates the omissionof transmission of torque through the second connecting mechanism.

The first-to-second mode switching speed variator may have a fixedinput-to-output speed ratio.

The power transmission apparatus may further include a second-to-firstmode switching speed variator which works to change speed of at leastone of the first and second rotors for compensating for a difference inspeed between the first and second rotors when the second operation modeis switched to the first operation mode to establish the mechanicalconnection between the first and second rotors. Specifically, an inputspeed of the first connecting mechanism may be identical with an outputspeed of the first connecting mechanism. This eliminates the omission oftransmission of torque through the first connecting mechanism.

The second-to-first mode switching speed variator may have a fixedinput-to-output speed ratio.

The torque transmission control mechanism may include anelectronically-controlled breaker which blocks the transmission oftorque between the first rotor and the internal combustion engine. Thismay avoid the transmission of torque from the first rotor to theinternal combustion engine before the internal combustion engine isstarted.

The torque transmission control mechanism may also include a one-waypower transmission mechanism which establishes the transmission oftorque between the first rotor and the internal combustion engine undercondition that speed of an input of the one-way power transmissionmechanism leading to the first rotor is higher than that of an output ofthe one-way power transmission mechanism leading to the internalcombustion engine, thereby avoiding the transmission of torque from theinternal combustion engine to the first rotor when the torque isproduced upon start of combustion of fuel in a combustion chamber of theinternal combustion engine. Usually, when the torque is produced by thecombustion of fuel in the internal combustion engine, the speed of arotating shaft (i.e., and output shaft) of the internal combustionengine rises quickly. The quick rise in speed of the rotating shaft willoccur in a short time. It is, therefore, very difficult or impossible todisconnect between the internal combustion engine and the first rotorafter the start of combustion of fuel is detected. When the quick risein speed is transmitted to the first rotor, it will result in pulsationof torque in the power transmission device. In order to avoid thisproblem, the one-way power transmission mechanism works not to transmitthe torque from the internal combustion engine to the first rotor whenthe speed of the internal combustion engine rises, so that the speed ofthe output of the one-way power transmission mechanism is higher thanthat of the input of the one-way power transmission mechanism, therebyeliminating the transmission of torque pulsation to an operator of thevehicle.

The power split device may be implemented by a single planetary gearset. Specifically, each of the first, second, and third rotors may beone of a sun gear, a carrier, and a ring gear.

According to the second aspect of the invention, there is provided apower transmission control system for a vehicle which comprises a powertransmission device and a controller. The power transmission deviceincludes (a) a power split device which includes a first, a second, anda third rotor which are rotate in conjunction with each other to splitpower among an electric rotating machine, an internal combustion engine,and a driven wheel of a vehicle, the first, the second, and the thirdrotor being so linked as to have rotational speeds thereof arrayed on astraight line in a nomographic chart, (b) a torque transmission controlmechanism which selectively establishes and blocks transmission oftorque between the first rotor and the internal combustion engine, (c) aconnecting mechanism which establishes a mechanical connection betweenthe second rotor and the third rotor, and (d) a speed variator which hasa variable input-to-output speed ratio. When the torque transmissioncontrol mechanism establishes the transmission of torque between thefirst rotor and the internal combustion engine, powers of the second andthird rotors are opposite in sign to each other. The controller actuatesthe torque transmission control mechanism to transmit torque, asproduced by the first rotor, to the internal combustion engine whenspeed of the internal combustion engine is lower than a given value.

The given value may be a typical idling speed of the internal combustionengine that is a minimum speed required to ensure the stability inoperation of the internal combustion engine.

According to the third aspect of the invention, there is provided apower transmission control system for a vehicle which comprises a powertransmission device and a controller. The power transmission deviceincludes (a) a power split device which includes a first, a second, anda third rotor which are rotate in conjunction with each other to splitpower among an electric rotating machine, an internal combustion engine,and a driven wheel of a vehicle, the first, the second, and the thirdrotor being so linked as to have rotational speeds thereof arrayed on astraight line in a nomographic chart, (b) a torque transmission controlmechanism which selectively establishes and blocks transmission oftorque between the first rotor and the internal combustion engine, (c) afirst connecting mechanism which establishes a mechanical connectionbetween the second rotor and the third rotor, (d) a second connectingmechanism which establishes a mechanical connection between the firstrotor and the second rotor, and (d) a speed variator which has avariable input-to-output speed ratio. When the torque transmissioncontrol mechanism establishes the transmission of torque between thefirst rotor and the internal combustion engine, powers of the second andthird rotors are opposite in sign to each other. The controller whichcontrols operations of the first and second connecting mechanism toswitch between a first and a second operation mode. The first operationmode is to establish the mechanical connection between the second andthird rotors through the first connecting mechanism and block themechanical connection between the first and second rotors through thesecond connecting mechanism. The second operation mode is to block themechanical connection between the second and third rotors through thefirst connecting mechanism and establish the mechanical connectionbetween the first and second rotors through the second connectingmechanism. The controller also works to inhibit both the first andsecond connecting mechanisms from establishing the mechanicalconnections, respectively, when a travel permission switch for thevehicle is in an off-state.

According to the fourth aspect of the invention, there is provided apower transmission control system for a vehicle which comprise a powertransmission device and a controller. The power transmission deviceincludes (a) a power split device which includes a first, a second, anda third rotor which are rotate in conjunction with each other to splitpower among an electric rotating machine, an internal combustion engine,and a driven wheel of a vehicle, the first, the second, and the thirdrotor being so linked as to have rotational speeds thereof arrayed on astraight line in a nomographic chart, (b) a torque transmission controlmechanism which selectively establishes and blocks transmission oftorque between the first rotor and the internal combustion engine, (c) afirst connecting mechanism which establishes a mechanical connectionbetween the second rotor and the third rotor, (d) a second connectingmechanism which establishes a mechanical connection between the firstrotor and the second rotor, and (d) a speed variator which has avariable input-to-output speed ratio. When the torque transmissioncontrol mechanism establishes the transmission of torque between thefirst rotor and the internal combustion engine, powers of the second andthird rotors are opposite in sign to each other. The controller controlsoperations of the first and second connecting mechanism to switchbetween a first and a second operation mode. The first operation mode isto establish the mechanical connection between the second and thirdrotors through the first connecting mechanism and block the mechanicalconnection between the first and second rotors through the secondconnecting mechanism. The second operation mode is to block themechanical connection between the second and third rotors through thefirst connecting mechanism and establish the mechanical connectionbetween the first and second rotors through the second connectingmechanism. The controller also works to control the input-to-outputspeed ratio of the speed variator so that a total input-to-output speedratio of a power transmission path extending from one of the internalcombustion engine and the electric rotating machine to the driven wheelto have values different between the first and second operation modes.The controller establishes the mechanical connections through the firstand second connecting mechanisms when a travel permission switch for thevehicle is turned off.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be understood more fully from the detaileddescription given hereinbelow and from the accompanying drawings of thepreferred embodiments of the invention, which, however, should not betaken to limit the invention to the specific embodiments but are for thepurpose of explanation and understanding only.

In the drawings:

FIG. 1( a) is a block diagram which illustrates a power transmissiondevice of the first embodiment of the invention which is installed in ahybrid system for a vehicle;

FIG. 1( b) is a view of power transmission paths of the powertransmission device of FIG. 1( a);

FIG. 2( a) is a schematic block diagram which shows a power transmissionpath when a vehicle is started by a motor-generator in a first operationmode;

FIG. 2( b) is a nomographic chart which represents an operation of apower split device of the power transmission device of FIG. 1( a) alongwith the speed of an internal combustion engine;

FIG. 2( c) is a table which lists a relation in sign of rotationaldirection, torque, and power among a sun gear, a carrier, and a ringgear of the power split device of FIGS. 2( a) and 2(b);

FIG. 3( a) is a schematic block diagram which shows a power transmissionpath when a vehicle is run by a motor-generator in a second operationmode;

FIG. 3( b) is a nomographic chart which represents an operation of apower split device along with the speed of an internal combustionengine;

FIG. 3( c) is a schematic block diagram which shows a modification ofthe power transmission path of FIG. 3( a) in which a vehicle torque istransmitted to a driven wheel without a CVT in a second operation mode;

FIG. 4( a) is a schematic block diagram which shows a power transmissionpath when an internal combustion engine is started by a motor-generatorin a second operation mode;

FIG. 4( b) is a nomographic chart which represents an operation of apower split device along with the speed of an internal combustionengine;

FIG. 4( c) is a table which lists a relation in sign of rotationaldirection, torque, and power among a sun gear, a carrier, and a ringgear of the power split device of FIGS. 4( a) and 4(b);

FIG. 5( a) is a schematic block diagram which shows a power transmissionpath when a vehicle is driven by an internal combustion engine in asecond operation mode;

FIG. 5( b) is a nomographic chart which represents an operation of apower split device along with the speed of an internal combustionengine;

FIG. 6( a) is a graph which shows a relation between a total gear ratioof a power transmission device of the first embodiment and a gear ratioof a CVT;

FIG. 6( b) is a graph which shows a relation between a total gear ratioof a power transmission device of the first embodiment and a powertransmission efficiency;

FIG. 7 is a block diagram which illustrates a power transmission deviceaccording to the second embodiment of the invention;

FIG. 8 is a block diagram which illustrates a modification of a powertransmission device which may be used in a structure of each of thefirst and second embodiment;

FIG. 9 is a block diagram which illustrates a second modification of apower transmission device which may be used in a structure of each ofthe first and second embodiment;

FIG. 10 is a view which illustrates a modification of a powertransmission device of the second embodiment;

FIG. 11 is a view which illustrates a second modification of a powertransmission device of the second embodiment;

FIG. 12 is a block diagram which illustrates a third modification of apower transmission device which may be used in a structure of each ofthe first and second embodiment;

FIG. 13( a) is a block diagraph which illustrates a fourth modificationof a power transmission device which may be used in a structure of eachof the first and second embodiment;

FIG. 13( b) is a view of power transmission paths of the powertransmission device of FIG. 13( a);

FIG. 14( a) is a block view which illustrates a fifth modification of apower transmission device which may be used in a structure of each ofthe first and second embodiment;

FIG. 14( b) is a view of power transmission paths of the powertransmission device of FIG. 14( a);

FIG. 15( a) is a schematic block diagram which shows a powertransmission path of a power transmission device when an internalcombustion engine is started by a motor-generator in a first operationmode;

FIG. 15( b) is a nomographic chart which represents an operation of apower split device of FIG. 15( a) along with the speed of an internalcombustion engine;

FIG. 16 is a view which shows an equivalent structure of a powertransmission device of FIG. 1( a) for explaining how to determine atotal gear ratio;

FIG. 17 is a flow chart of a program which may be executed by a powertransmission device of the first embodiment when a vehicle is stopped;and

FIG. 18 is a flow chart of a modified program which may be executed by apower transmission device of the first embodiment when a vehicle isstopped.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to the drawings, wherein like reference numbers refer to likeparts in several views, particularly to FIGS. 1( a) and 1(b), there isshown a hybrid system equipped with a power transmission control systemaccording to the first embodiment of the invention. The powertransmission control system is equipped with a power transmission deviceand a controller working to control an operation of the powertransmission device.

FIG. 1( a) illustrates the structure of the hybrid system. FIG. 1( b) isa skeleton view of power transmission paths.

The hybrid system includes a motor-generator 10 and a power split device20. The motor-generator 10 is made of a three-phase ac motor-generatorand works as an in-vehicle power producing device along with an internalcombustion engine 12 to run an automotive vehicle. The power splitdevice 20 works to split power or torque among the motor-generator 10,the internal combustion engine (e.g., a gasoline engine) 12, and drivenwheels 14 of the vehicle.

The power split device 20 is equipped with a single planetary gear set70 made up of three power split rotors: a sun gear S, a carrier C, and aring gear R. To the sun gear S, an output axis (i.e. a rotating shaft)10 a of the motor-generator 10 is coupled mechanically. The ring gear Ris also connected mechanically to the sun gear S through a continuouslyvariable transmission (CVT) 22, a clutch C2, and a gear G5. Themotor-generator 10 is, therefore, connected mechanically to the ringgear R through the CVT 22, the clutch C2, and the gear G5. In otherwords, the motor-generator 10 and the ring gear R are so connectedthrough a mechanical interlocking path that they rotate in conjunctionwith each other without through the other power split rotors of thepower split device 20. The CVT 36, as used in this embodiment, is of amechanical type using a metallic or rubber belt. The gear G5 isimplemented by a counter gear which works to change a ratio ofrotational speed of an input to an output thereof by a fixed factor andreverse the direction of rotation of the input, other words, reverse thesign in direction of rotation of the output to that of the input. Theclutch C2 works as an electronically controlled hydraulic power breakerto block transmission of power or torque between an input and an outputthereof. The input and the output, as referred to therein, an input intowhich the energy is entered and an output from which the energy goesout, but its relation may be changed.

The motor-generator 10 may alternatively be coupled mechanically to ajunction between the clutches C1 and C2 through a power transmissionpath 10 b, as indicated by a broken line in FIG. 1( a). This layout ofthe motor-generator 10 is denoted in FIG. 1( b) by “MG” circled by abroken line. In this case, when it is required to run the driven wheels14 by means of the motor-generator 10, the power produced by themotor-generator 10 is, as will be described later in detail, transmittedto the driven wheels 14 only through the clutch C2 and the gear G6. Thismode is suitable for a high-speed running of the vehicle. The designermay determine whether the motor-generator 10 is connected to the clutchC2 through or without the CVT 22 in terms of desired travel function ofthe vehicle.

To the ring gear R of the power split device 20, the driven wheels 14are coupled mechanically. Specifically, the driven wheels 14 are joinedto the ring gear R through gears G5 and G6 and a differential gear 24.The gear G6 is implemented a forward gear set (also called a normalrotation gear set) which works to change a ratio of rotational speed ofan input to an output thereof by a fixed factor, but does not reversethe direction of rotation of the input.

To the carrier C of the power split device 20, the sun gear S is coupledmechanically through gears G2α and G2β, a clutch C1, and the CVT 22. Thegears G2α and G2β are each implemented by a counter gear which works tochange a ratio of rotational speed of an input to an output thereof by afixed factor and reverse the direction of rotation of the input. Thegears G2α and G2β may be made by a single gear assembly or gear box.

The clutch C1 works as an electronically controlled hydraulic powerbreaker to block transmission of power or torque between an input and anoutput thereof. The clutches C1 and C2 are, as can be seen from FIG. 1(b), each joined at either of the input or the output thereof to a commonrotational shaft.

The crankshaft (i.e., the rotating shaft 12 a) of the engine 12 is alsocoupled mechanically to the carrier C through a one-way bearing 26 and aclutch C3. The one-way bearing 26 works as a one-way transmissionmechanism to permit the transmission of power (torque) from the carrierC to the engine 12 under the condition that the rotational speed of thecarrier C is not lower than that of the rotating shaft 12 a of theengine 12. In other words, the one-way bearing 26 works to have the sungear S follow an input of the one-way bearing 26 unless the speed of anoutput of the one-way bearing 26 is greater than that of the input ofthe one-way bearing 26. The clutch C3 works as a normally-open type ofelectronically controlled mechanical breaker to block the transmissionof power (torque) between an input and an output thereof.

The sun gear S is also coupled mechanically to the rotating shaft 12 aof the engine 12 through a one-way bearing 28. Like the one-way bearing26, the one-way bearing 28 works as a one-way transmission mechanism topermit the transmission of power (torque) from the engine 12 to the sungear S under the condition that the speed of the rotating shaft 12 a ofthe engine 12 is not lower than the speed of the sun gears S. In otherwords, the one-way bearing 28 works to have the sun gears S follow therotation of the rotating shaft 12 a of the engine 12 unless the speed ofan output of the one-way bearing 28 is greater than that of an input ofthe one-way bearing 28. Therefore, the engine 12 is permitted to bejoined mechanically to the ring gear R through the one-way bearing 28,the CVT 22, the clutch C2, and the gear G5.

Each of the gears G2α, G2β, G5, and G6 may be implemented by a gear setmade up of a plurality of gears with a fixed gear ratio (i.e., aninput-to-output speed ratio).

The hybrid system also includes a controller 40 to control an operationof the power transmission device. The controller 40 works to actuate theclutches C1, C2, and C3 and the CVT 22 to control the mode of powertransmission and determine a controlled variable of the engine 12. Thecontroller 40 also works to control an operation of an inverter (i.e., apower converter) 42 to determine a controlled variable of themotor-generator 10.

The power transmission device is so designed as to operate selectivelyeither in a first operation mode or a second operation mode. In thefirst operation mode, the clutch C1 is in an engaged state, while theclutch C2 is in a disengaged state. In the second operation mode, theclutch C1 is in the disengaged state, while the clutch C2 is in theengaged state. The operations of the power transmission device in thefirst and second operation modes and a sequence of running states of thevehicle when the first operation mode is switched to the secondoperation mode will be described below, respectively. Note that theclutches C1 and C2 and the CVT 22 are illustrated in FIG. 1( a) as beingseparate from each other, but either or both of the clutches C1 and C2and the CVT 22 may be assembled into a unit functioning as a connectingmechanism.

First Operation Mode

The first operation mode is a starting mode in which a vehicle startingoperation is made by the motor-generator 10. The first operation modewill be described below with reference to FIGS. 2( a) to 2(c). FIG. 2(a) illustrates a power transmission path when the vehicle is started.FIG. 2( b) is a nomographic chart which represents the operation of thepower split device 20 along with the speed of the internal combustionengine 12. In FIG. 2( b), a negative direction of rotation of the ringgear R is defined as “forward” because the gear G5 is made of a countergear. Arrows in nomographic chart indicate directions of torque.

In the example of FIGS. 2( a) and 2(b), the clutch C3 is in thedisengaged state, and the internal combustion engine 12 is stopped. Thespeeds of the rotors of the planetary gear set 70 which constitute thepower split device 20 are dependent on the speed of the motor-generator10 and the gear ratio (also called an output-to-input speed ratio, avariable speed ratio, a pulley ratio, or a CVT ratio) of the CVT 22.Specifically, in the nomographic chart of FIG. 2( b), the speeds of thesun gears S, the carrier C, and the ring gear S lie on a diagonalstraight line. In other words, the sun gear S, the carrier C, and thering gear R are so linked as to provide output rotational energiesthereof which are arrayed straight in the nomographic chart. The speedof the ring gear R that is one of the rotors of the power split device20 other than the sun gear S and the carrier C is, therefore, set bydetermining the speed of the sun gear S and the carrier C.

The hybrid system of this embodiment is capable of selecting the gearratio (i.e., a speed ratio) of the CVT 22 to achieve the so-calledgeared neutral which places the speed of the driven wheels 14 at zero(0) in the first operation mode during running of the motor-generator10. Specifically, the power split device 20 is so designed that amountsof output rotational energy (i.e., power) of the sun gear S and thecarrier C that are the power split rotors of the planetary gear set 70other than the ring gear R are, as illustrated in FIG. 2( c), oppositein sign to each other, so that the power is circulated between the sungear S and the carrier C through a looped mechanical path. Therefore,when the geared neutral is established to place the speed of the drivenwheels 14 at zero (0), it will cause the power inputted to the sun gearS to be outputted from the carrier C and then inputted to the sun gear Sagain In other words, when the power split device 20 is in the gearedneutral, the amount of rotational energy (i.e., power) outputted to thedriven wheels 14 will be zero (0). When the power is not circulatedthrough the looped mechanical path extending through the sun gear S andthe carrier C, it will cause the output energy of the motor-generator 10to be consumed fully as thermal energy in the power split device 20according to the energy conservation law. This will result inimpractical structure of the power split device 20 which does not workto split the power, in other words, in which the rotors do not functionas power split rotors of the power split device 20. When the gearedneutral is established in the hybrid system of this embodiment, it willcause the power to be recirculated inevitably in the power split device20. The looped path extending from the carrier C to the sun gear S needsnot continue mechanically completely. For instance, the looped path maybe a path which has a disconnected portion to be closed selectively by aclutch to enable the rotational energy to be recirculated. Note that inFIG. 2( c), the plus (+) and minus (−) signs of the rotational directionof each of the sun gear S, the carrier C, and the ring gear R representopposite directions: a normal direction and a reverse direction thereof,the plus (+) sign of the rotational energy (i.e., power) indicates whenthe rotational energy is outputted from the power split device 20, andthe plus (+) and minus (−) signs of the torque are so defined as to meetthe condition that the product of signs of the rotational direction andthe torque will be the sign of the rotational energy (i.e., power).

The structure of the power transmission device of this embodiment isdesigned to enable the motor-generator 10 to produce a higher degree oftorque when starting the vehicle without need for increasing the size ofthe motor-generator 10. This is for the following reasons.

If a ratio of the number Zs of teeth of the sun gear S to the number Zrof teeth of the ring gear R (i.e., Zs/Zr) of the power split device 20is defined as ρ, a ratio of the speed Nc of the carrier C to the speedof the motor-generator 10 (i.e., the speed Ns of the sun gear S) (i.e.,Ns/Nc) is defined as β, and torques of the ring gear R, the sun gear S,the carrier C, and the motor-generator 10 are defined as Tr, Ts, Tc, andTm, respectively, equations, as listed below, are met.

Tr=−Tc/(1+ρ)  (c1)

Ts=−ρTc/(1+ρ)  (c2)

β(Tm+Ts)=Tc  (c3)

Eliminating torques Ts and Tc from Eq. (c3) using Eqs. (c1) and (c2), weobtain

Tr=(β/ρ)Tm/{(1/ρ)−1−β}  (c4)

Eq. (c4) shows that a great increase in torque Tr of the ring gear R(i.e., the output axis of the power split device 20), in other words,the torque to be transmitted to the driven wheels 14 is achieved byapproximating the ratio β to (1/ρ)−1. This ensures the torque requiredto start the vehicle without need for increasing the size of themotor-generator 10.

Second Operation Mode

FIG. 3( a) illustrates a power transmission path of the powertransmission device in the second operation mode that is an EV travelmode in which the vehicle is run only by the motor-generator 10. FIG. 3(b) is a nomographic chart in the second operation mode. The clutch C3 isin the disengaged state.

The power is transmitted from the motor-generator 10 to the drivenwheels 14 through the CVT 22, the clutch C2, and the gear G6 without thepower split device 20. This is because torque is not transmitted to thecarrier C of the power split device 20, so that torque is also notinputted, as can be seen from Eqs. (c1) and (c2), to the sun gear S andthe ring gear R.

FIG. 3( c) illustrates a modification of the transmission path of FIG.1( a). In the illustrated structure, the motor-generator 10 is connecteddirectly to the clutch C2 instead of being coupled through the CVT 22,as illustrated in FIG. 1( a). The torque, as produced by themotor-generator 10, is transmitted to the driven wheels 14 through theclutch C2 and the gear G6.

FIG. 4( a) illustrates a power transmission path of the powertransmission device when the engine 12 is started in the secondoperation mode. FIG. 4( b) illustrates a nomographic chart in such anengine starting mode.

The clutch C3 is engaged, as shown in FIG. 4( a), to enable the torqueto be transmitted to the engine 12 through the power split device 20.Specifically, the rotational energy of a starting rotor (i.e., thecarrier C) of the power split device 20 is transmitted to the rotatingshaft 12 a of the engine 12 through the one-way bearing 26. FIG. 4( c)demonstrates relations among the rotational direction, the torque, andthe power of the sun gear S, the carrier C, and the ring gear R in theengine starting mode. The sun gear S and the ring gear R are opposite insign of the power to each other, so that the power is circulated betweenthe sun gear S and the ring gear R. Therefore, the carrier C may berotated at a very low or zero (0) speed, or the absolute value of thepower of the carrier C may be decreased to a small value even when theabsolute value of output torque of the motor-generator 10 or the drivenwheels 14 is not zero (0). This enables the speed of the input of theone-way bearing 26 relative to that of the output thereof to be loweredextremely when the clutch C3 is engaged while the rotating shaft 12 a ofthe engine 12 is stopped, thereby minimizing mechanical vibrations ofthe power split device 20 which arises from the switching of the clutchC3 to the engaged state.

It is preferable that the clutch C3 is engaged when the speed of theengine 12 is lower than or equal to a minimum value required to ensurethe stability in running of the engine 12. When the speed of the engine12 is above the minimum value, the controller 40 starts to burn fuel inthe internal combustion engine 12 being running and control the burningof fuel in a combustion control mode.

FIG. 5( a) illustrates a power transmission path of the powertransmission device to run the vehicle through the engine 12 in thesecond operation mode. FIG. 5( b) illustrates a nomographic chart insuch an engine-powered running mode.

When the speed of the engine 12 is increased, and the speed of the inputof the one-way bearing 28 reaches that of the output thereof, it willcause the torque of the engine 12 to be outputted from the one-waybearing 28. The transmission of torque between the motor-generator 10and the driven wheels 14 or between the engine 12 and the driven wheels14 without the power split device 20 is achieved by disengaging theclutch C3. The output of the engine 12 or the motor-generator 10 isconverted in speed by the CVT 22 and then transmitted to the drivenwheels 14.

When the vehicle is being run by the engine 12, the motor-generator 10does not necessarily need to be operated as an electric motor, but maybe used as a generator.

Switching from First Operation Mode to Second Operation Mode

FIG. 6( a) illustrates a relation between a total gear ratio (i.e., atotal output-to-input speed ratio) of the power transmission pathextending from the motor-generator 10 or the engine 12 to the drivenwheels 14 and the gear ratio of the CVT 22 when the driven wheels 14 arerun by the motor-generator 10 or the engine 12. The gear ratio, asreferred to herein, may also be expressed by either of anoutput-to-input speed ratio or an input-to-output speed ratio dependingupon which of the input speed and the output speed is considered to be abasis. When the first operation mode is entered, the controller 40 maychange the gear ratio of the CVT 22 continuously to change the directionin which the vehicle travels from the backward to the forward direction.When a given gear ratio of the CVT 22 is reached, the operation mode ofthe power transmission device is switched to the second operation mode,thereby increasing a range in which the total gear ratio is permitted tobe changed.

Specifically, the power transmission device is capable of changing thegear ratio of the CVT 22 in the first operation mode, as demonstrated inFIG. 6( a), to change the rotational direction of the driven wheels 14from the backward direction to the forward direction continuouslythrough the instant where the speed of the driven wheels 14 is zero andsubsequently changing the gear ratio of the CVT 22 further to increasethe total gear ratio in a power transmission path from themotor-generator 10 to the driven wheels 14. When the time the omissionof the transmission of torque will not occur is reached, in other words,a mode-switching point P is reached, the power transmission device isoperable to switch the first operation mode to the second operation modeand then turn the CVT 22 in the opposite direction (which will also bereferred to as a CVT reversing operation below) to increase the totalgear ratio further.

The above operation is achieved by selecting the direction in which thetotal gear ratio changes with a change in gear ratio of the CVT 22 inthe second operation mode to be opposite that in the first operationmode. This is established in the condition that a derivative value of afunction in which the gear ratio of the CVT 22 is expressed by anindependent variable, and the total gear ratio is expressed by adependent variable with respect to the gear ratio of the CVT 22 in thesecond operation mode is opposite in sign to that in the first operationmode. This condition is realized by the gears G2α, G2β, and G5.Specifically, the possibility of the CVT reversing operation isdependent upon the sign of a product of gear ratios of the gears G2α,G2β, and G5. Conditions in which the CVT reversing operation is feasiblewill be given by a section “TOTAL GEAR RATIO”, as will be discussed inthe last section of this application.

The controller 40 performs the above first-to-second operation modeswitching under the condition that the total gear ratio, that is, aratio of an output speed that is the speed of the driven wheels 14 to aninput speed that is the speed of the motor-generator 10 or the engine 12is not changed. This condition is met when speeds of an input and anoutput of the clutch C1 are identical with each other, and speeds of aninput and an output of the clutch C2 are identical with each other. Thefirst-to-second operation mode switching may, therefore, be made throughthe time when both the clutches C1 and C2 are engaged simultaneously,thus avoiding the omission of transmission of torque to the drivenwheels 14.

The omission of transmission of torque to the driven wheels 14 isavoided by the means of the gears G2α, G2β, and G5. The planetary gearset 70 (i.e., the power transmission device 20) is, as described above,so constructed that the speeds of the sun gear S, the carrier C, and thering gear R of the power split device 20 are either all identical withor all different from each other. Specifically, the power split device20 is, as can be seen from FIG. 2( a), so designed that the speeds ofrotation (or the rotational directions) of the sun gear S and the ringgear R are opposite in sign to each other in the nomographic chart. Thesun gear S, the carrier C, and the ring gear R are, thus, different inspeed from each other except when they are all zero (0). It is,therefore, impossible for only the CVT 30 to realize the condition thatspeeds of the input and the output of the clutch C1 are identical witheach other, and speeds of the input and the output of the clutch C2 areidentical with each other. Accordingly, the power transmission device ofthis embodiment has the gear G5, G2α, and G2β to ensuring the stabilityin engagement of the clutches C1 and C2 without the omission oftransmission of torque to the driven wheels 14. Specifically, the gearG5 disposed between the ring gear R of the power split device 20 and theclutch C2 serves as a fist-to-second operation mode switching speedvariator to compensate for a difference in speed between the sun gear Sand the ring gear R when the first operation mode is switched to thesecond operation mode. The gear G5 may alternatively disposed betweenthe sun gear S and the clutch C2. Similarly, either or both of the gearsG2α and G2β disposed between the carrier C of the power split device 20and the clutch C1 serve as a second-to-first operation mode switchingspeed variator to compensate for a difference in speed between the sungear S and the carrier C when the second operation mode is switched tothe first operation mode. The gear ratios (i.e. input-to-output speedratios) of the gears G2α, G2β, and G5 and the CVT 22 required to avoidthe omission of transmission of torque to the driven wheels 14 will bediscussed later in the section “TOTAL GEAR RATIO”.

As apparent from the above discussion, the switching from the firstoperation mode to the second operation mode results in an increasedrange in which the total gear ratio is permitted to be changed. Thisallows the CVT 22 to be reduced in size. In the second operation mode,the power is not circulated, thus enabling the power transmissionefficiency that is the ratio of input energy to output energy in thepower transmission device to be increased as compared with in the firstoperation mode. FIG. 6( b) is a graph which represents a relationbetween the power transmission efficiency and the total gear ratio. Thegraph shows that a very low range of the power transmission efficiencyexists in the first operation mode, but not in the second operationmode. In the graph of FIG. 6( b), the power transmission efficiency inthe first operation mode immediately before switched to the secondoperation mode is illustrated as being higher than that in the secondoperation mode, but it does not mean that the power transmissionefficiency when the power transmission device is designed to operateonly in the first operation mode is higher than when the powertransmission device is designed to be switched between the first andsecond operation modes.

The controller 40 actuates the power transmission device in the firstoperation mode to permit the driven wheels 14 to be rotated in theforward and backward directions and stopped as needed without having tochange the sign of speed (i.e., the direction of rotation) of themotor-generator 10 even though the power transmission efficiency is low.The controller 40 switches from the first operation mode to the secondoperation mode in a range where the speed of the driven wheels 14 ishigher than a given value, thereby improving the power transmissionefficiency and increasing the range where the total gear ratio ispermitted to be changed. When the power transmission device is switchedto the second operation mode, it results in no need for the power splitdevice 20 to transmit the power to the driven wheels 14, but the carrierC of the power split device 20 may be used to apply initial torque(i.e., starting torque) to the engine 12. In other words, when it isrequired to start the engine 12 in the second operation mode, one of therotors of the planetary gear set 70 which needs not be used intransmitting the power to the driven wheels 14 may be employed to startthe engine 12.

The structure of the hybrid system (i.e., the power transmission device)of this embodiment offers the following advantages.

1) The power transmission device is so designed that when it is requiredto output torque from an engine starting rotor (i.e., the carrier C) ofthe power split device 20 to start the engine 12, the power will becirculated between the other power split rotors (i.e., the sun gear Sand the ring gear R), thereby facilitating ease of decreasing the speedof the engine starting rotor (i.e., the carrier C) to a very low speedor zero (0), which will minimize mechanical vibrations exerted on thepower split device 20 when the initial torque is applied to the engine10.2) In the second operation mode, the power split rotors of the powersplit device 20 other than the engine starting rotor (i.e., the carrierC) are coupled mechanically together through the CVT 22. This permitsthe inclination of the straight line on which the power split rotors arearrayed in speed in the nomographic chart, as already described, to bechanged by controlling the gear ratio of the CVT 22, in other words, thespeed of the engine starting rotor (i.e., the carrier C) to becontrolled variably by selecting the gear ratio of the CVT 22 regardlessof the speed of the driven wheels 14.3) In the second operation mode, the clutch C3 is in the disengagedstate except when the engine 12 is started, thereby permitting the powerto be transmitted from the motor-generator 10 or the engine 12 to thedriven wheels 14 without the power split device 20.4) When it is required to transmit the output of the motor-generator 10to the driven wheels 14 in the second operation mode, the CVT 22 isdisposed in connection between the motor-generator 10 and the drivenwheels 14, thus permitting the speed of the motor-generator 10 to bechanged by the CVT 22.5) The engine 12 is placed in power transmitting communication with thesun gear S and the CVT 22 to transmit power of the engine 12 to the sungear S and the CVT 22 after start-up of the engine 12. In other words,the engine starting rotor (i.e., the carrier C) which is to be placed inpower transmitting communication with the rotating shaft 12 a when it isrequired to start the engine 12 is different from a power transmittedrotor (i.e., the sun gear S) which is to be placed in power transmittingcommunication with the engine 12 and to which the power is transmittedfrom the engine 12 when it is required to rotate the driven wheels 14,thus enabling the speed of the engine 12 to be brought to an effectivespeed range quickly. The power transmitted to the sun gear S is hardlyoutputted from the ring gear R. Most of the power is transmitted to thedriven wheels 14 through the CVT 22.6) When it is required to transmit the output of the engine 12 to thedriven wheels 12 in the second operation mode, the CVT 22 is disposed inconnection between the engine 12 and the driven wheels 14, thuspermitting the speed of the engine 12 to be changed by the CVT 22.7) The one-way bearing 28 is disposed between the engine 12 and the sungear S to establish the transmission of torque from the engine 12 to thesun gears S under the condition that the speed of the input of theone-way bearing 28 (i.e., the speed of the rotating shaft 12 a of theengine 12) is not lower than that of the output of the one-way bearing28 (i.e., the speed of the sun gear S), thus causing the torque to betransmitted from the engine 12 to the sun gear S when the speed of theinput of the one-way bearing 28 reaches that of the output thereof. Thisfacilitates the ease of starting to supply the torque of the engine 12to the sun gear S.8) The switching between the first operation mode and the secondoperation mode makes mechanical connections among the motor-generator10, the engine 12, and the driven wheels 14 suitable for operationalconditions thereof.9) The power transmission device is so designed that when the sign ofthe speed of the motor-generator 10 (or the engine 12) is fixed to beeither plus or minus, the signs of power of the carrier C and the sungear S will be opposite to each other in the first operation mode, whilethe powers of the sun gear S and the ring gear R will be zero (0) in thesecond operation mode. This causes the power to be circulated betweenthe rotors of the power split device 20 other than connectedmechanically to the driven wheels 14 in the first operation mode, thuspermitting the geared neutral to be established desirably. The power isnot circulated in the second operation mode, thus resulting in anincrease in power transmission efficiency. No need also arises toreverse the motor-generator 12 (or the engine 10) upon the switchingbetween the first and second operation modes.10) The CVT 22 is operable both in the first and second operation modes,thus resulting in a decrease in part of the power transmission device.11) A first order derivative value of a function, in which the gearratio of the CVT 22 is expressed by an independent variable, and thetotal gear ratio in the power transmission path between the power source(i.e., the motor-generator 10 or the engine 12) and the driven wheels14) is expressed by a dependent variable, with respect to the gear ratioof the CVT 22 (i.e., the independent variable) in the second operationmode is set opposite in sign to that in the first operation mode. Thisenables the CVT reversing operation to broaden the range in which thetotal gear ratio is permitted to be changed.12) The power transmission device is equipped with a mechanical measure(i.e., the gears G2α, G2β, and G5) which compensates for a difference inspeed between the carrier C and the ring gear R, thereby eliminating theinstantaneous omission of transmission of torque to the driven wheels 14upon the switching between the first operation mode and the secondoperation mode.13) The power transmission device is equipped with theelectronically-controlled clutch C3 to establish or block thetransmission of torque between the engine starting rotor (i.e., thecarrier C) of the power split device 20 and the rotating shaft 12 a ofthe engine 12, thereby avoiding an error in transmission of torque fromthe engine starting rotor to the engine 12 before the engine 12 isstarted, which minimizes consumption of energy or power in the powertransmission device.14) The power transmission device is also equipped with the one-waybearing 26 which establishes the transmission of torque from the powerslit device 20 to the rotating shaft 12 a of the engine 12 under thecondition that the speed of the input of the one-way bearing 26 (i.e.,the speed of the engine starting rotor) is not lower than that of theoutput of the one-way bearing 26 (i.e., the speed of the rotating shaft12 a of the engine 12), thereby avoiding the transmission of torque fromthe engine 12 to the engine starting rotor when the torque is producedupon start of combustion of fuel in a combustion chamber of the engine12, so that the speed of the rotating shaft 12 a of the engine 12 risesquickly. This is because when the speed of the output of the one-waybearing 26 (i.e., the speed of the rotating shaft 12 a) is elevatedabove that of the input of the one-way bearing 26, the one-way bearing26 blocks the transmission of torque from the output to the input of theone-way bearing 26. This avoids the transmission of torque pulsation tothe operator of the vehicle.15) The clutches C1 and C2 are, as illustrated in FIG. 1( b), coupleddirectly to the common shaft of the power transmission device, thusfacilitating the ease of arranging the clutches C1 and C2 close to eachother, which permits the size of the power transmission device to bereduced.

FIG. 7 illustrates a hybrid system according to the second embodiment ofthe invention. The same reference numbers as employed in FIG. 1 refer tothe same or similar parts, and explanation thereof in detail will beomitted here.

An conditioner A/C (i.e., a vehicle accessory) is installed in thehybrid vehicle and powered by the power split device 20. The airconditioner A/C is equipped with a compressor 44 which has a drivenshaft connected mechanically to the sun gear S of the power split device20, so that the torque is supplied from the sun gears S to the drivenshaft of the compressor 44. The power transmission device is, asdescribed above, capable of rotating the sun gear S at speeds other thanzero (0) when the driven wheels 14 are at rest and thus running the airconditioner A/C when the vehicle is parked.

The hybrid system of this embodiment is capable of keeping theefficiency in operation of the motor-generator 10 high when actuatingthe compressor 44 while the vehicle is stopped. This is achieved by thestructure which ensures the torque required to start the vehicle withouthaving to increase the size of the motor-generator 10. In other words,the structure of the power transmission device of this embodimenteliminates the need for increasing the size of the motor-generator 10 toactuate the air conditioner A/C. In this embodiment, a maximum amount ofpower required to be outputted from the motor-generator 10 to thecompressor 44 is 25% to 50% of a maximum amount of power to be outputtedfrom the motor-generator 10. The efficiency of the motor-generator 10usually decreases as the output therefrom decreases in a range up to acertain output which is smaller than a maximum output of thegenerator-motor 10. Therefore, the efficiency of the motor-generator 10is enabled to be kept high when the motor-generator 10 is run only fordriving the compressor 44. A maximum output of motor-generators such asones mounted in conventional hybrid vehicles is usually 50 kW or morewhich is ten or more than dozen times a maximum required output of thecompressor 44 (e.g., several kW). This causes the motor-generator 10 tobe run to drive the compressor 44 with a low efficiency when the vehicleis at a stop.

When a required output of the motor-generator 10 is increased with aincrease in required traveling performance of the vehicle, the output ofthe motor-generator 10 may be used mainly to run the vehicle by limitingthe amount of energy to drive the compressor 44. Such an increase inoutput of the motor-generator 10 is usually required to enhance thedrivability of the vehicle when being accelerated. The increase in sizeof the motor-generator 10 in order to meet such a requirement leads togreat concern about an increase in production cost thereof. In contrast,the structure of the power transmission device of this embodiment maywork to restrict the energy or power required to drive the compressor 44to ensure the ability to accelerate the vehicle without having toincrease the size of the motor-generator 10, which results inimprovement on the drivability of the vehicle.

The joining of the compressor 44 to the sun gear S does not impinge onthe circulation of power, as described in the first embodiment, at all.The structure of the power transmission device of this embodiment,therefore, has the same advantages as those in the first and secondoperation modes in the first embodiments.

This embodiment also offers an additional beneficial effect below.

16) The use of the power split device 20 as a power source for thecompressor 44 eliminates the need for an additional electric motor todrive the compressor 44.

Other Embodiments

The power transmission devices of the above embodiments may be modifiedas discussed below.

Type of Speed Variator

The CVT 22 needs not be of a belt-type. For example, a traction drivetype or hydraulic continuously variable transmission may be used.Alternatively, a gear transmission may be used instead of the CVT 22.

Joint Between Motor-Generator and Power Split Device

Mechanical joints among the motor-generator 10, the engine 12, thedriven wheels 14, and the power split rotors (i.e., the sun gear S, thecarrier C, and the ring gear R) may be modified as shown in FIG. 8.

FIG. 8 illustrates the mechanical joints among parts of the powertransmission device in the case where the power split device 20 is madeonly of a single planetary gear set. The clutch C3 is coupled to theinput of the one-way bearing 26, but may alternatively be connected tothe output of the one-way bearing 26. All possible combinations of thepower split rotors x, y, and z of the power split device 20 (i.e., thesun gear S, the carrier C, and the ring gear R) are (x, y, z)=(S, C, R),(S, R, C), (C, S, R), (C, R, S), (R, S, C), and (R, C, S).

By using some of the gears G2 to G13 in the power transmission device,the circulation of power between the power split rotors x and y isachieved in the first operation mode or between the power split rotors yand z in the second operation mode when the clutch C3 is engaged.Additionally, the omission of transmission of torque to the drivenwheels 14 or the CVT reversing operation is also achieved by using someof the gears G2 to G13 in the power transmission device.

Each of the gears G2 to G13 may be implemented by a speed increasinggear set, a speed reducing gear set, or a counter gear whose gear ratiois fixed. Each of the gears G2 to G13 may alternatively be implementedby a mechanism using a chain or a belt.

The motor-generator 10 may alternatively be, as illustrated in FIG. 9,coupled mechanically to a junction between the one-way bearing 28 andthe CVT 22, a junction between the clutches C1 and C2, or a junctionbetween the clutch 22 and the driven wheels 14. In the case where thepower split rotors x, y, and z of the power split device 20 are, like inFIG. 8, the carrier C, the sun gear S, and the ring gear R,respectively, the arrangements of the motor-generator 10, as denoted by“MG” on the left side and the middle of the drawing, correspond to thoseof FIG. 1( a) and FIG. 1( c), respectively. All possible combinations ofthe power split rotors x, y, and z of the power split device 20 are (x,y, z)=(S, C, R), (S, R, C), (C, S, R), (C, R, S), (R, S, C), and (R, C,S). The motor-generator 10 may be, as clearly shown in FIG. 9, joinedmechanically to one of the input of the CVT 22, the junction between theclutches C1 and C2, and the output of the clutch C2. FIG. 9 omits gearsfor sake of convenience. FIGS. 10 and 11 are skeleton views whichillustrate modifications of the mechanical connections of themotor-generator 10 to parts of the power transmission device. In FIG.11, the motor-generator 10 is installed between the clutches C1 and C2.

FIG. 12 illustrates a modification of the mechanical joints of themotor-generator 10, the engine 12, and the driven wheels 14 to the powersplit rotors x, y, and z of the power split device 20. The clutches C1and C2 are disposed one in each of two power transmission pathsextending between the power split device 20 and the driven wheels 14.Like in the above modifications, all possible combinations of the powersplit rotors x, y, and z of the power split device 20 are (x, y, z)=(S,C, R), (S, R, C), (C, S, R), (C, R, S), (R, S, C), and (R, C, S).

Layout of Speed Variator (CVT 22)

The speed variator, i.e., the CVT 22 needs not necessarily be disposedat a location useful both in the first and second operation modes, butmay be utilized in either of the first and second operation modes.Instead of the CVT 22, the power transmission device may be equippedwith a plurality of speed variators one or more of which are used in thefirst operation mode, and remaining one or more of which are used in thesecond operation mode. For instance, in the structure of FIG. 8, a firstvariator may be disposed between the power split rotors x and y, while asecond variator may be disposed between the power split rotors y and z.

Power Split Rotors

The power split device 20, as used in the above embodiments, is sodesigned that when the signs of rotational speeds (i.e., directions ofrotation) of the sun gear S and the ring gear R are opposite each other,the speed of the carrier C is zero (0), but may alternatively bedesigned that when the signs of rotational speeds of the sun gear S andthe ring gear R are identical with each other, the speed of the carrierC is zero (0). This is realized by, for example, a double pinionplanetary gear set such as one, as disclosed in Japanese Patent FirstPublication No. 2001-108073.

FIGS. 13( a) to 14(b) illustrate examples in which the power splitdevice 20 is equipped with the double pinion planetary gear set. Thesame reference numbers, as employed in the above embodiments, refer tothe same or similar parts. The gear G2 is a counter gear. The gears G4and G5 are a forward gear (also called a normal rotation gear).

The power split device 20 may be made only by a differential gear or toadditionally include it.

Torque Transmission Control Mechanism

The torque transmission control mechanism which establishes or blocksthe transmission of torque from the engine starting rotor (i.e., thecarrier C) of the power split device 20 to the rotating shaft 12 a tostart the engine 12 is made up of the clutch C3 and the one-way bearing26, but may alternatively be equipped with only the clutch C3. In thiscase, unwanted transmission of torque which will be increased usuallysuddenly upon start of combustion of fuel in the engine 12 to the powerslit device 20 may be avoided by disengaging the clutch C3 prior to thestart of combustion of fuel after an initial rotation is given to therotating shaft 12 a of the engine 12. The torque transmission controlmechanism may also be made by only the one-way bearing 26. In the casewhere the engine 12 is permitted to rotate only in one direction, thepower transmission device 20 is actuated only in a range where the signof speed (i.e., the rotational direction) of the engine starting rotor(i.e., the carrier C) connected mechanically to the input of the one-waybearing 26 is not reversed.

The clutch C3 may alternatively be joined to the output of the one-waybearing 26.

Instead of the one-way bearing 26 which transmits torque to the engine12 when the speed of the engine starting rotor (i.e., the carrier C) ofthe power split device 20 is greater than that of the rotating shaft 12a of the engine, a one-way clutch or another similar type mechanismworking to have the rotating shaft 12 a follow the rotation of theengine starting rotor of the power split device 20 with or without anyslip may be used.

The clutch C3 which selectively blocks the transmission of torque fromthe power split device 20 to the rotating shaft 12 a to start the engine12 is of a normally open type, but may be of a normally closed type.

Torque Applying Mechanism

Instead of the one-way bearing 28 working as a torque applying mechanismto connect the power transmitted rotor (i.e., the sun gear S of thepower slit device 20 to the rotating shaft 12 a of the engine 12 toapply torque, as produced by the engine 12, to the driven wheels 14, aone-way clutch may be used. A one-way power transmitting mechanism whichhas an output member following rotation of an input member thereofleading to the rotating shaft 12 a of the engine 12 with or without anyslip may be used to transmit torque from the engine 12 to the drivenwheels 14 when the speed of the input member coupled to the engine 12 ishigher than that of the output member coupled to the power split device20.

Instead of the one-way power transmitting mechanism, a clutch may beused. It is advisable that the clutch be engaged when speeds of theinput and output members have been brought into agreement with eachother by controlling speeds of the engine 12 and the power transmittedrotor of the power split device 20 in order to minimize mechanicalvibrations of the power split device upon engagement of the clutch.

Accessory Powered by Torque of Power Split Rotor

In addition to the compressor 44 of the air conditioner, the power splitdevice 20 may be connected to supply power to a brake pump whichproduces hydraulic pressure for applying braking force to the drivenwheels 14, a water pump for coolant of the engine 12, or a cooling fanfor the engine 12.

Power Split Rotor Coupled to Accessory

One of the power split rotors other than the sun gear S, as illustratedin FIG. 7, may be coupled mechanically to the accessory (also called anauxiliary device) such as the compressor 44 installed in the vehicle.The accessory may be connected mechanically between the clutch C3 andthe one-way bearing 26 in FIG. 7. This connection will result in thecirculation of power in the second operation mode even at a time otherthan when the engine 12 is started, thus leading to a decrease in powertransmission efficiency, but offering the advantages that the speed ofthe carrier C is permitted to be adjusted to zero (0) or another valuewhile the vehicle is running and that the power is permitted to besupplied to the accessory both in the first and second operation modeseven when the vehicle is stopped.

Engine Starting Operation

The engine 12 may alternatively be started in the first operation mode.Specifically, the controller 40 may start the engine 12 when the vehicleis stopped and then use the power to move the vehicle. FIG. 15( a)illustrates a power transmission path of the power transmission deviceof the first embodiment when starting the engine 12 in the firstoperation mode. FIG. 15( b) illustrates a nomographic chart when theengine 12 is started while the vehicle is at a stop. When it is requiredto start the engine 12, the controller 40 engages the clutch C2 totransmit the power from the carrier C to the rotating shaft 12 a of theengine 12. After the engine 12 is fired up, the torque, as produced bythe engine 12, is transmitted to the driven wheels 14 through theone-way bearing 28 and the power split device 20 to start the vehicle.The power transmission device of this structure is enabled to establishthe geared neutral in the first operation mode which keeps the speed ofthe driven wheels 14 at zero (0) even when the torque is transmittedfrom the engine 12 through the one-way bearing 28. This eliminates theneed for a torque converter. The engine 12 may alternatively be startedin the second operation mode.

The engine 12 may also be started regardless of whether the powertransmission device is in the first or second operation mode. Forexample, the controller 40 may start the engine 12 when the clutches C1and C2 are both disengaged. Specifically, the controller 40 locks thedriven wheels 14 through a brake when the vehicle is at a stop, engagesthe clutch C3, and actuates the motor-generator 10 to supply the powerfrom the motor-generator 10 to the rotating shaft 12 a of the engine 12through the power split device 20, the one-way bearing 26, and theclutch C3.

The power of the carrier C needs not necessarily be outputted from thepower split device 20 to start the engine 12 after a difference in speedbetween the carrier C and the rotating shaft 12 a is placed below agiven value. When such a speed difference is greater than the givenvalue, the controller 40 may increase the degree of engagement of theclutch C3 gradually, in other words, keep the clutch C3 in a partiallyengaged state and then supply the power to the rotating shaft 12 a.

Condition to Engage Clutch C3

When the speed of the engine 12 is below a minimum value needed toensure the stability in operation of the engine 12, and an enginestarting request is made, the controller 40 engages the clutch C3 in theabove embodiments, but may alternatively make such engagement when it isrequired to brake the vehicle. This is enabled in the structure of thefirst and second embodiments designed to ensure the engine startingtorque even when the motor-generator 10 is reduced in size. Thereduction in size of the motor-generator 10 to a degree that generatesup to several tens kW may result in a difficulty in increasing thebraking force to be produced by a regenerative operation of themotor-generator 10 to a required level. However, the power transmissiondevice of the first or second embodiment is enabled to engage the clutchC3 and exert a resistive load from the engine 12 to the power splitdevice 20 to produce engine braking.

When Vehicle is Stopped or Towed

When the vehicle is stopped or towed, the controller 40 preferablydisengages the clutches C1 and C2. This avoids the rotation f the CVT 22following the towing of the vehicle, thereby minimizing thedeterioration of the CVT 22 even equipped with a metal belt. Forexample, in the structure of FIG. 1, when the controller 40 disengagesboth the clutches C1 and C2, it causes the generator-motor 10 to holdthe CVT 22 from rotating, and permits the clutches C1 and C2 to idle.Basically, such an operation is achieved both in the first and secondoperation modes by the structure of the power transmission device inwhich the CVT 22 is disposed in a looped path extending between the twopower split rotors of the power split device 20, and the motor-generator10 is joined mechanically to one of the ends of the CVT 22. FIG. 17shows a sequence of logical steps which may be executed by thecontroller 40 of the first embodiment at a regular interval when thevehicle is stopped.

After entering the program, the routine proceeds to step 10 wherein itis determined whether a travel permission switch 95 is turned off ornot. The travel permission switch 95 is a switch to be turned on or offby a vehicle operator to permit the vehicle to travel. The travelpermission switch 95 may be designed to be turned on or off in awireless fashion when a portable wireless device carried by the vehicleoperator is close to a vehicle controls system equipped with thecontroller 40. For example, when the travel permission switch 95 isturned on, the inverter 42 is connected electrically to a storagebattery installed in the vehicle. If a YES answer is obtained meaningthat the travel permission switch 95 is in the off-state, then theroutine proceeds to step 12 wherein the controller 40 disengages theclutch C1 and C2. If a NO answer is obtained in step 10 or after step12, the routine terminates.

The controller 40 may engage the clutch C1 and C2 and then set the totalgear ratio of the power transmission device to a given high-speed gearratio or alternatively change the gear ratio of the CVT 22 to havevalues different between the first and second operation modes and thenengage the clutches C1 and C2, thereby locking the driven wheels 14.FIG. 18 shows a modification of a sequence of logical steps which may beexecuted by the controller 40 of the first embodiment at a regularinterval when the vehicle is stopped. The same step numbers as employedin FIG. 17 refer to the same operations, and explanation thereof indetail will be omitted here.

If a YES answer is obtained in step 10 meaning that the travelpermission switch 95 is turned off, then the routine proceeds to step 14wherein the controller 40 regulates the gear ratio of the CVT 22 to setthe total gear ratio to a given high-speed gear ratio or alternativelychanges the gear ratio of the CVT 22 to have values different betweenthe first and second operation modes. The routine then proceeds to step16 wherein the controller 40 engages the clutches C1 and C2. If a NOanswer is obtained in step 10 or after step 16, the routine terminates.

Other Modifications

The power transmission device in each of the first and secondembodiments is, as described above, equipped with the engine startingrotor to be placed in power transmitting communication with the rotatingshaft 12 a to start the engine 12 and the power transmitted rotor to beplaced in power transmitting communication with the rotating shaft 12 ato permit the power to be transmitted from the engine 12 which aredifferent from each other, but alternatively be designed to have amodification of the structure of FIG. 1 which includes a one-way powertransmission mechanism which permits the power to be transmitted betweenthe engine 12 and the carrier C when the speed of the engine 12 ishigher than that of the carrier C and a clutch which selectively blocksthe transmission of power between the engine 12 and the carrier C. Inthis case, the carrier C serves as both the engine starting rotor andthe power transmitted rotor.

The power transmission device may be designed to allow the omission oftransmission of torque to the driven wheels 14 upon switching betweenthe first and second operation modes. This also offers the sameadvantage 1), as described in the first embodiment. Specifically, thecontroller 40 increases the degree of engagement of one of the clutchesC1 and C2 gradually which is to be switched from the disengaged state tothe engaged state to establish the partial engagement of the one of theclutches C1 and C2. However, when a fail-safe mode is entered in whichit is required to switch between the first and second operation modesquickly regardless of mechanical stock arising therefrom, the controller40 may switch between the first and second operation modes forcibly at agear ratio of the CVT 22 which develops values of the total gear ratiowhich are different between the first and second operation modes withoutcreating the partial engagement of the one of the clutches C1 and C2.

The CVT reversing operation needs not necessarily be performed uponswitching between the first and second operation modes. For instance,the power transmission device may be so designed that the circulation ofpower is established in the first operation mode, but not in the secondoperation mode. The switching from the first operation mode to thesecond operation mode will improve the power transmission efficiency.

The power transmission device in each of the first and secondembodiments connects the motor-generator 10 to the sun gear Smechanically without through the CVT 22, but may be designed to have amodification of the structure of FIG. 8 in which the motor-generator 10is disposed between the CVT 22 and the clutches C1 and C2.

The clutches C1 and C2 need not necessarily be of a hydraulic controlledtype. For instance, the clutches C1 and C2 may be implemented by anelectromagnetic clutch, a tooth clutch, or a dog clutch. In this case,the ease of layout of the clutches C1 and C2 is also achieved byconnecting the clutches C1 and C2 together through a single commonshaft.

The clutches C1 and C2 need not necessarily be joined to the singlecommon shaft, but may be joined independently of each other. This alsooffers the same advantage 1), as described above.

The power transmission device may alternatively be equipped with aplurality of electric rotating machines for use in running the vehicle.The electric rotating machines may be all or partly implemented bymotor-generators. For example, some of the electric rotating machinesmay be made of electric motors, while the other electric rotatingmachines may be made of electric generators which also work to charge ahigh-voltage battery installed in the vehicle to supply electric powerto the electric motors. For example, in case of use of an additionalelectric rotating machine in the structure of FIG. 1, it may be disposedbetween the ring gear R of the power split device 20 and the gear G5.

The electric rotating machine may alternatively be implemented by abrushed DC motor or an induction motor.

The power transmission device may switch from the second operation modeto the first operation mode when the total gear ration remainedunchanged between the first and second operation modes duringdeceleration of the vehicle. The vehicle may be subjected to the stopcontrol operation, as described above, in the second operation mode.

Total Gear Ratio

The total gear ratio in the power transmission device of the firstembodiment may be determined using an equivalent structure, asillustrated in FIG. 16. The illustrated structure has gears G1, G2, andG4. The gear G1 corresponds to the CVT 22. The gear G2 serves as acombination of the gears G2α and G2β of the first embodiment between theclutch C1 and the carrier C. In the following discussion, a total gearratio of the gears G2α and G2β is given by a gear ratio r2 of the gearG2. A gear ratio r4 of the gear G4 is one (1).

The gear ratio rn of the gear Gn (n=1, 4 to 6) is defined as a ratio ofspeed b to speed a. Note that each of “a” and “b” in each block of FIG.16 indicates one of an input and an output of each gear. The number ofteeth of the sun gear S/the number of teeth of the ring gear R isdefined as a gear ratio ρ. The rotational speeds of the sun gear S, thering gear R, and the carrier C are defined as wS, wR, and wC,respectively. Equation (c5) is met.

ρwS−(1+ρ)wC+wR=0  (c5)

1 Total Gear Ratio in First Operation Mode

In the first operation mode, the speed wS of the sun gear S and thespeed wC of the carrier C have the following relation.

wC=r1·r2·wS  (c6)

The speed wG6b of an output of the gear G6 is given by Eq. (7) below.

wG6b=r6·r5·wR  (c7)

By substituting Eqs. (c6) and (c7) into Eq. (c5), we obtain

wG6b=r6·r5·{r1·r2(1+ρ)−ρ}wS  (c8)

Therefore, the total gear ratio is given by Eq. (c9) below.

Total gear ratio=r6·r5·{r1·r2(1+ρ)−ρ}  (c9)

2 Total Gear Ratio in Second Operation Mode

The total gear ratio in the second operation mode is given by Eq. (c10)below in a power transmission path extending through the gears G1, G4,and G6.

Total gear ratio=r1·r4·r6  (c10)

3 Mode Switching Condition without Omission of Transmission of Torque

No omission of transmission of torque is achieved under condition wherethe speed wG1b of the gear G1 is equal to both the speed wG2a of thegear G2 and the speed wG4a of the gear G4. This condition is expressedby

wC/r2=wS·r1=wR·r5/r4  (c11)

Expressing the speeds wS and wR of the sun gear S and the ring gear R bythe speed wC of the carrier C in Eq. (c11), and substituting it into Eq.(c5), we obtain

r1=ρr5/{r2r5·(1+ρ)−r4}  (c12)

The switching between the first and second operation modes with noomission of transmission of torque to the driven wheels 14 is,therefore, achieved by selecting the gear ratio r1 of the CVT 22 (i.e.,the gear G1 in FIG. 16) to have the value in the right side of Eq.(c12).

CVT Reversing Operation

The CVT reversing operation is achieved under condition that the productof values derived by differentiating a function in which the total gearratio is expressed by a dependent variable, and the gear ratio r1 isexpressed by an independent variable with respect to the gear ratio r1in the first operation mode and in the second operation mode isnegative.

Using Eqs. (c9) and (c10), the above condition is given by

{r6·r5·r2·(1+ρ)}·{r4·r6}<0

Rewriting the above relation, we obtain

r5·r4·r2<0  (c13)

Since, in the structure of the first embodiment, the gear G5, G2α, andG2β are counter gears, and the gear G4 is omitted, r2>0, r5<0, and r4=1.

The total gear ratio in the structure of FIG. 8 may also be determinedin the same manner as described above.

While the present invention has been disclosed in terms of the preferredembodiments in order to facilitate better understanding thereof, itshould be appreciated that the invention can be embodied in various wayswithout departing from the principle of the invention. Therefore, theinvention should be understood to include all possible embodiments andmodifications to the shown embodiments witch can be embodied withoutdeparting from the principle of the invention as set forth in theappended claims.

What is claimed is:
 1. A power transmission control system for a vehiclecomprising: a power transmission device including (a) a power splitdevice which includes a first, a second, and a third rotor which arerotate in conjunction with each other to split power among an electricrotating machine, an internal combustion engine, and a driven wheel of avehicle, the first, the second, and the third rotor being so linked asto have rotational speeds thereof arrayed on a straight line in anomographic chart, (b) a torque transmission control mechanism whichselectively establishes and blocks transmission of torque between thefirst rotor and the internal combustion engine, (c) a first connectingmechanism which establishes a mechanical connection between the secondrotor and the third rotor, (d) a second connecting mechanism whichestablishes a mechanical connection between the first rotor and thesecond rotor, and (d) a speed variator which has a variableinput-to-output speed ratio, wherein when the torque transmissioncontrol mechanism establishes the transmission of torque between thefirst rotor and the internal combustion engine, powers of the second andthird rotors are opposite in sign to each other; and a controller whichcontrols operations of the first and second connecting mechanism toswitch between a first and a second operation mode, the first operationmode being to establish the mechanical connection between the second andthird rotors through the first connecting mechanism and block themechanical connection between the first and second rotors through thesecond connecting mechanism, the second operation mode being to blockthe mechanical connection between the second and third rotors throughthe first connecting mechanism and establish the mechanical connectionbetween the first and second rotors through the second connectingmechanism, the controller also working to control the input-to-outputspeed ratio of the speed variator so that a total input-to-output speedratio of a power transmission path extending from one of the internalcombustion engine and the electric rotating machine to the driven wheelto have values different between the first and second operation modes,the controller establishing the mechanical connections through the firstand second connecting mechanisms when a travel permission switch for thevehicle is turned off.